Surface shape recognition sensor and method of manufacturing the same

ABSTRACT

A surface shape recognition sensor includes a plurality of capacitive detection elements, a support electrode, and a protective film. The capacitive detection elements are formed from lower electrodes and a deformable plate-like upper electrode made of a metal. The lower electrodes are insulated and isolated from each other and stationarily laid out on a single plane of an interlevel dielectric formed on a semiconductor substrate. The upper electrode is laid out above the lower electrodes at a predetermined interval and has a plurality of opening portions. The support electrode is laid out around the lower electrodes while being insulated and isolated from the lower electrodes, and formed to be higher than the lower electrodes to support the upper electrode. The protective film is formed on the upper electrode to close the opening portions. The opening portions of the upper electrode are laid out in a region other than regions on a main part of the lower electrode and on the support electrode. A method of manufacturing the surface shape recognition sensor is also disclosed.

BACKGROUND OF THE INVENTION

[0001] The present invention relates to a surface shape recognitionsensor used to sense a surface shape having a fine three-dimensionalpattern such as a human fingerprint or animal noseprint.

[0002] Along with the progress in information-oriented society in theenvironment of the current society, the security technology has receiveda great deal of attention. For example, in the information-orientedsociety, a personal authentication technology for establishment of,e.g., an electronic cash system is an important key. Authenticationtechnologies for preventing theft or illicit use of credit cards havealso been extensively researched and developed (e.g., Yoshimasa Shimizuet al., “A Study on the Structure of a Smart Card with the Function toVerify the Holder”, Technical Report of IEICE OFS92-32, pp. 25-30(1992-11)).

[0003] There are various kinds of authentication schemes such asfingerprint authentication and voice authentication. Especially, manyfingerprint authentication techniques have been developed so far.Fingerprint authentication schemes are roughly classified into anoptical reading scheme and a scheme of using the human electriccharacteristic and detecting the three-dimensional pattern of the skinsurface of a finger and replacing it with an electrical signal.

[0004] In the optical reading scheme, fingerprint data is read mainlyusing reflection of light and an image sensor (CCD) and collated (e.g.,Seigo Igaki et al., Japanese Patent Laid-Open No. 61-221883). A schemeof reading a pressure difference by the three-dimensional pattern of theskin surface of a finger using a piezoelectric thin film has also beendeveloped (e.g., Masanori Sumihara et al., Japanese Patent Laid-Open No.5-61965).

[0005] An authentication scheme of replacing a change in electriccharacteristic due to contact of a skin with an electrical signaldistribution by detecting a resistive or capacitive change amount usinga pressure sensitive sheet so as to detect a fingerprint has also beenproposed (e.g., Kazuhiro Itsumi et al., Japanese Patent Laid-Open No.7-168930).

[0006] In the above prior arts, however, the optical reading scheme isdifficult to make a compact and versatile system, and its applicationpurpose is limited. The scheme of detecting the three-dimensionalpattern of the skin surface of a finger using a pressure sensitive sheetor the like is difficult to put into practical use or is unreliablebecause a special material is required and fabrication is difficult.

[0007] “Marco Tartagni” et al. have developed a capacitive fingerprintsensor using an LSI manufacturing technology (Marco Tartagni and RobertGuerrieri, A 390 dpi Live Fingerprint Imager Based on FeedbackCapacitive Sensing Scheme, 1997 IEEE International Solid-State CircuitsConference, pp. 200-201 (1997)).

[0008] In this fingerprint sensor, the three-dimensional pattern of askin is detected using a feedback static capacitance scheme by a sensorchip in which small capacitive detection sensors are two-dimensionallyarrayed.

[0009] In the capacitive detection sensor, two plates are formed on theuppermost layer of an LSI, and a passivation film is formed on theplates. In this capacitive detection sensor, a skin surface functioningas a third plate is isolated by an insulating layer formed from air, andsensing is performed using the difference in distance, thereby detectinga fingerprint. As characteristic features of a fingerprintauthentication system using this structure, no special interface isnecessary, and a compact system can be constructed, unlike theconventional optical scheme.

[0010] In principle, a fingerprint sensor using a capacitive detectionsensor is obtained by forming a lower electrode on a semiconductorsubstrate and forming a passivation film on the resultant structure. Acapacitance between the skin and the sensor is detected through thepassivation film, thereby detecting the fine three-dimensional patternof the skin surface of a finger.

[0011] In this sensor chip using capacitive detection sensors, however,since a skin serves as one electrode for capacitive detection, staticelectricity generated at the fingertip readily causes electrostaticdestruction in an integrated circuit such as a sensor circuitincorporated in the sensor chip.

[0012] To prevent the above-described electrostatic destruction of anelectrostatic capacitance fingerprint sensor, a surface shaperecognition sensor having an electrostatic capacitive detection sensorhaving a sectional structure as shown in FIG. 15 has been proposed. Thesensor shown in FIG. 15 will be described. The sensor has a lowerelectrode 1503 formed on a semiconductor substrate 1501 via aninterlevel dielectric 1502, a plate-shaped deformable upper electrode1504 which is separated from the lower electrode 1503 at a predeterminedinterval, and a support electrode 1505 laid out around the lowerelectrode 1503 to support the upper electrode 1504 while being insulatedand isolated from the lower electrode 1503.

[0013] In the sensor having the above arrangement, when a finger to besubjected to fingerprint detection comes into contact with the upperelectrode 1504, the pressure from the finger deflects the upperelectrode 1504 toward the lower electrode 1503 to change theelectrostatic capacitance formed between the lower electrode 1503 andthe upper electrode 1504. This change in electrostatic capacitance isdetected by a detection circuit (not shown) on the semiconductorsubstrate 1501 through an interconnection (not shown) connected to thelower electrode 1503. In this surface shape recognition sensor, when theupper electrode 1504 is grounded through the conductive supportelectrode 1505, static electricity generated at the fingertip anddischarged to the upper electrode 1504 flows to ground through thesupport electrode 1505. For this reason, the detection circuitincorporated under the lower electrode 1503 is protected fromelectrostatic destruction.

[0014] The above-described deformable upper electrode must be formedwith a space under it. An example of a sensor using such a hollowstructure is described in a “method of manufacturing a capacitivepressure sensor for detecting a change in pressure by a change inelectrostatic capacitance” by “P. Rey et al.” (reference 1: P. Rey, P.Charvet, M. T. Delaye, and S. Abouhassan, “A High Density CapacitivePressure Sensor Array For Fingerprint Sensor Application”, proceedingsof Transducers '97, pp. 1453-1456 (1997)).

[0015] To form such a hollow structure, a lower electrode is formed, andthen, a sacrificial film is formed on the lower electrode. An upperelectrode and a deformable portion to which the upper electrode is fixedare formed on the sacrificial film. After that, the sacrificial filmunder the deformable portion is removed by etching from the sides of theedge portion of the deformable portion to which the upper electrode isfixed, thereby forming a space under the upper electrode. In such a finehollow structure, however, since the height of the space under thedeformable portion is as small as about 0.5 to 2 μm, though thedeformable portion generally has a length of about 50 μm in the lateraldirection, it is very difficult to completely remove the sacrificialfilm by etching from the lateral direction. Additionally, in theabove-described surface shape recognition sensor, since a plurality ofcells formed from a single lower electrode are arrayed, it is almostimpossible to completely remove the sacrificial film by etching from thelateral direction.

[0016] To the contrary, when an opening portion is formed in thedeformable portion formed on the sacrificial film, and the sacrificialfilm is removed by etching through the opening portion, the sacrificialfilm can be efficiently removed. Hence, the sacrificial film can becompletely removed.

[0017] When the upper electrode serving as a deformable portion has anopening portion, a foreign substance or the like may enter the hollowstructure from the opening portion to impede the detection operation ofthe sensor. This may also cause an error in the lower electrode. Hence,in such a surface shape recognition sensor, to close (seal) the openingportion, a protective film is formed on the upper electrode.

[0018] However, the opening portion poses a problem in forming aprotective film for protecting the upper electrode on the upperelectrode. As the protective film, an inorganic dielectric film such asa silicon oxide film or silicon nitride film is preferably used becauseof its characteristics. A film of such a material is generally formed bydeposition such as CVD or sputtering. This method is easy to apply.However, when a protective film of an insulating material is formed onthe upper electrode with an opening portion by, e.g., CVD, theinsulating material enters the hollow structure from the opening portionof the upper electrode. When the insulating material enters the hollowstructure to form a structure made of the insulating material, thesensor operation may be impeded by this structure in some cases.

SUMMARY OF THE INVENTION

[0019] The present invention has been made to solve the above problems,and has as its object to easily form a protective film on an upperelectrode by a generally used method that is easy to apply in a surfaceshape recognition sensor for which a hollow structure can easily beformed by forming an opening portion in the upper electrode.

[0020] In order to achieve the above object, according to the presentinvention, there is provided a surface shape recognition sensorcomprising a plurality of capacitive detection elements formed fromlower electrodes and a deformable plate-like upper electrode made of ametal, the lower electrodes being insulated and isolated from each otherand stationarily laid out on a single plane of an interlevel dielectricformed on a semiconductor substrate, and the upper electrode being laidout above the lower electrodes at a predetermined interval and having aplurality of opening portions, a support electrode laid out around thelower electrodes while being insulated and isolated from the lowerelectrodes, and formed to be higher than the lower electrodes to supportthe upper electrode, and a protective film formed on the upper electrodeto close the opening portions, wherein the opening portions of the upperelectrode are laid out in a region other than regions on a main part ofthe lower electrode and on the support electrode.

BRIEF DESCRIPTION OF THE DRAWINGS

[0021]FIGS. 1A to 1G are views for explaining a method of manufacturinga surface shape recognition sensor according to an embodiment of thepresent invention;

[0022]FIGS. 2A to 2F are views for explaining the method ofmanufacturing the surface shape recognition sensor according to theembodiment of the present invention;

[0023]FIGS. 3A and 3B are views for explaining the method ofmanufacturing the surface shape recognition sensor according to theembodiment of the present invention;

[0024]FIGS. 4A to 4C are views for explaining the method ofmanufacturing the surface shape recognition sensor according to theembodiment of the present invention,

[0025]FIGS. 5A to 5E are views for explaining a method of manufacturinga surface shape recognition sensor according to another embodiment ofthe present invention;

[0026]FIGS. 6A to 6F are views for explaining a method of manufacturinga surface shape recognition sensor according to still another embodimentof the present invention;

[0027]FIGS. 7A to 7G are views for explaining a method of manufacturinga surface shape recognition sensor according to still another embodimentof the present invention;

[0028]FIGS. 8A and 8B are schematic sectional views for explaining theoperative states of a surface shape recognition sensor according tostill another embodiment of the present invention;

[0029]FIGS. 9A and 9B are schematic sectional views for explaining theoperative states of a surface shape recognition sensor according tostill another embodiment of the present invention;

[0030]FIGS. 10A to 10C are schematic sectional views for explaining theoperative states of a surface shape recognition sensor according tostill another embodiment of the present invention;

[0031]FIG. 10D is a graph showing the characteristic of the surfaceshape recognition sensor according to the embodiment shown in FIGS. 10Ato 10C;

[0032]FIGS. 11A to 11C are schematic sectional views for explaining theoperative states of a surface shape recognition sensor according tostill another embodiment of the present invention;

[0033]FIG. 11D is a graph showing the characteristic of the surfaceshape recognition sensor according to the embodiment shown in FIGS. 11Ato 1C;

[0034]FIGS. 12A to 12C are schematic sectional views for explaining theoperative states of a surface shape recognition sensor according tostill another embodiment of the present invention;

[0035]FIG. 12D is a graph showing the characteristic of the surfaceshape recognition sensor according to the embodiment shown in FIGS. 12Ato 12C;

[0036]FIG. 13A is a schematic sectional view for explaining the state ofa surface shape recognition sensor according to still another embodimentof the present invention;

[0037]FIG. 13B is a schematic plan view for explaining the state of thesurface shape recognition sensor according to the embodiment shown inFIG. 13A;

[0038]FIG. 13C is a graph showing the characteristic of the surfaceshape recognition sensor according to the embodiment shown in FIGS. 13Aand 13B;

[0039]FIGS. 14A and 14B are plan views showing the structure of adeformable electrode of a surface shape recognition sensor according tostill another embodiment of the present invention; and

[0040]FIG. 15 is a schematic sectional view showing the structure of asurface shape recognition sensor having a deformable electrode.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0041] The embodiments of the present invention will be described belowwith reference to the accompanying drawings.

[0042] <First Embodiment>

[0043]FIGS. 1A to 3B explain a method of manufacturing a surface shaperecognition sensor according to an embodiment of the present invention.The manufacturing method will be described below with reference to FIGS.1A to 3B. First, as shown in FIG. 1A, an interlevel dielectric 110 a isformed on a substrate 101 made of a semiconductor material such assilicon. Another integrated circuit such as a detection circuit (notshown) having an interconnection structure with a plurality ofinterconnections is formed on the substrate 101 under the interleveldielectric 110 a.

[0044] After formation of the interlevel dielectric 101 a, a seed layer102 having a two-layered structure including a 0.1-μm thick titaniumfilm and a 0.1-μm thick gold film is formed by vapor deposition or thelike.

[0045] Next, as shown in FIG. 1B, a 5-μm thick resist pattern 103 havingan opening portion 103 a is formed on the seed layer 102. The resistpattern 103 is formed by known photolithography. After the resistpattern 103 is formed, a 1-μm thick metal pattern 104 formed from a goldplating film is formed on the seed layer 102 exposed to the openingportion 103 a by electroplating.

[0046] After the resist pattern 103 is removed, a 5-μm thick resistpattern 105 having an opening portion 105 a is newly formed, as shown inFIG. 1C. At this time, the metal pattern 104 is covered with the resistpattern 105. After the resist pattern 105 is formed, a 3-μm thick metalpattern 106 formed from a gold plating film is formed on the seed layer102 exposed to the opening portion 105 a by electroplating.

[0047] After the resist pattern 105 is removed, the seed layer 102 isselectively etched using the metal patterns 104 and 106 as a mask. Inthis etching, first, the upper layer of the seed layer 102, i.e., thegold film is selectively removed using an etchant containing iodine,ammonium iodide, water, and ethanol. Next, the lower layer of the seedlayer 102, i.e., the titanium film is selectively removed using anHF-based etchant. In wet etching of gold, the etching rate is 0.05μm/min.

[0048] As a result, as shown in FIG. 1D, a lower electrode 104 a with anupper layer formed from gold and a support electrode 106 a insulated andisolated from the lower electrode 104 a are formed on the substrate 101.The support electrode 106 a supports a deformable electrode (upperelectrode) (to be described later) and is formed in, e.g., a latticeshape on the substrate 101, as shown in the plan view of FIG. 1G. Aplurality of lower electrodes 104 a are respectively laid out in thecentral portions of regions surrounded by the lattice-shaped supportelectrode 106 a. The shape of the support electrode 106 a is not limitedto the lattice shape. For example, a plurality of support electrodeseach having a rectangular columnar shape with a square bottom surfacemay be laid out around each lower electrode 104 a (e.g., on linesextended from four corners).

[0049] As shown in FIG. 1E, a photosensitive resin film 107 is formed onthe substrate 101 by spin coating to cover the lower electrode 104 a andsupport electrode 106 a. The resin film 107 has a positivephotosensitivity. The resin film 107 is prepared by, e.g., adding apositive photosensitive material to a base resin such as polyamide,polyamide acid, or polybenzoxazole (or a precursor thereof).

[0050] The resultant resin film 107 is heated by keeping the substrate101 placed on a hot plate heated to about 120? C. for about 4 min.

[0051] Next, the region on the support electrode 106 a is exposed byknown photolithography. Subsequently, development processing isexecuted, thereby forming, in the resin film 107, an opening portion 107a to which the upper portion of the support electrode 106 a is exposed,as shown in FIG. 1F. After development processing, the resin film 107 isheated to about 310? C. and thermally cured.

[0052] The cured resin film 107 is etched back by chemical mechanicalpolishing to form a sacrificial film 117 having a flat surface, as shownin FIG. 2A. At this time, the upper surface of the support electrode 106a is almost flush with the surface of the sacrificial film 117. Theupper surface of the support electrode 106 a is exposed.

[0053] As shown in FIG. 2B, a seed layer 108 having a two-layeredstructure including a 0.1-μm thick titanium film and a 0.1-μm thick goldfilm is formed by vapor deposition or the like on the sacrificial film117 which is flattened to expose the upper surface of the supportelectrode 106 a.

[0054] As shown in FIG. 2C, a resist pattern 109 is formed. A 0.4-μmthick metal film 110 formed from a gold plating film is formed on theseed layer 108 exposed to the region without the resist pattern 109 byelectroplating. After the resist pattern 109 is removed, the seed layer108 is selectively etched and removed using the formed metal film 110 asa mask.

[0055] In this etching, first, the upper layer of the seed layer 108,i.e., the gold film is selectively removed using an etchant containingiodine, ammonium iodide, water, and ethanol. Next, the lower layer ofthe seed layer 108, i.e., the titanium film is selectively removed usingan HF-based etchant. In wet etching of gold, the etching rate is 0.05μm/min.

[0056] As a result, as shown in FIG. 2D, a deformable electrode (upperelectrode) 111 having a plurality of opening portions 111 a is formed.As shown in FIG. 2F, the opening portions 111 a are formed at the fourcorners of a rectangular region surrounded by the lattice-shaped supportelectrode 106 a. The opening portions 111 a need not always be formed atthe four corners of the opening region of the lattice and only need belaid out on the region between the support electrode 106 a and the lowerelectrode 104 a. In other words, the opening portions 111 a only needsto be laid out in a region other than the regions on the supportelectrode 106 a and lower electrode 104 a. The opening portions 111 aare preferably separated from the region on the lower electrode 104 a asfar as possible but preferably do not overlap the support electrode 106a.

[0057] The substrate 101 with the completed deformable electrode 111 isexposed to a plasma mainly containing oxygen gas. An etching speciesgenerated by the plasma is brought into contact with the sacrificialfilm 117 through the opening portions 111 a to remove the sacrificialfilm 117. Consequently, as shown in FIG. 2E, a space is formed under thedeformable electrode 111 which is supported by the support electrode 106a. A structure in which the deformable electrode 111 and lower electrode104 a are separated by the space is formed.

[0058] As shown in FIG. 3A, polyimide is coated to the deformableelectrode 111 and thermally cured to form a protective film 112 having athickness of about 1 tm. Thermal curing is executed at 300?C. for 30min. Since the deformable electrode 111 has the opening portions 111 a,the coated polyimide partially enters the space under the deformableelectrode 111 from the opening portions 111 a. However, since theopening portions 111 a are formed not on the lower electrode 104 a butnear the support electrode 106 a, the part of polyimide that has enteredthe space does not enter the space on the lower electrode 104 a.

[0059] Next, as shown in FIG. 3B, a projection 113 is formed in a regionof the protective film 112 above the lower electrode 104 a. Theprojection 113 is formed by forming a 5- to 10-μm thick photosensitivepolyimide film, exposing a region other than the structure An formationregion by known photolithography, developing the region, and annealingthe resultant structure at about 300? C. for about 30 min to thermallycure the film.

[0060] In the surface shape recognition sensor formed in theabove-described way, whose portion is shown in FIG. 3B, when a fingertipportion comes into contact with the protective film 112, the projection113 is pressed downward in accordance with the skin surface shape of thefinger in contact to deform the deformable electrode 111. Hence, thecapacitance formed between the deformable electrode 111 and the lowerelectrode 104 a changes. When halftone data is obtained incorrespondence with the change in capacitance formed on each lowerelectrode 104 a according to the skin surface shape, the skin surfaceshape can be reproduced. Capacitive detection or conversion intohalftone data is done by, e.g., an integrated circuit (not shown) formedon the substrate 101.

[0061] In this embodiment, the protective film 112 is formed after theopening portions 111 a are formed in the deformable electrode 111.However, the material of the protective film 112 does not enter thespace on the lower electrode 104 a. For this reason, even when theprotective film 112 is formed, the state wherein the space withoutanything is formed between the deformable electrode 111 and the lowerelectrode 104 a is held. Hence, the deformable electrode 111 can bedeformed by a downward force applied to the projection 113.

[0062] As described above, according to this embodiment, in the surfaceshape recognition sensor in which a hollow structure can easily beformed by forming the opening portions in the deformable electrode 111,as shown in FIG. 3B, the protective film can more easily be formed onthe deformable electrode by a generally used method, i.e., coating ofpolyimide, that is easy to apply.

[0063] <Second Embodiment>

[0064] Another embodiment of the present invention will be describednext. In the above embodiment, the protective film 112 is formed bycoating polyimide. However, the present invention is not limited tothis. For example, an inorganic insulating material such as siliconoxide may be formed by vapor deposition, as will be described below. Themanufacturing process will be described below. First, as has beendescribed with reference to FIGS. 1A to 2E, a space is formed under adeformable electrode 111 which is supported by a support electrode 106 asuch that the deformable electrode 111 and lower electrode 104 a areseparated by the space.

[0065] Next, as shown in FIG. 4A, a 3-μm thick silicon oxide film 412 isformed on the deformable electrode 111. To form the silicon oxide film412, CVD, plasma CVD, or ozone TEOS can be used. At the initial stage offormation of the silicon oxide film on the deformable electrode 111, thesilicon oxide film is formed such that it is formed only almostimmediately under opening portions 111 a to immediately close theopening portions 111 a. When the silicon oxide film 412 is formed thick,steps due to the presence of the opening portions 111 a are reduced.

[0066] As shown in FIG. 4B, the silicon oxide film 412 is etched back byabout 2 μm to form a 1-μm thick protective film 412 a on the deformableelectrode 111. As shown in FIG. 4C, a projection 113 is formed in aregion of the protective film 412 a above the lower electrode 104 a.

[0067] As described above, in this embodiment as well, the protectivefilm 412 a can be formed on the deformable electrode 111, as in theabove-described embodiment. In addition, even when the opening portions111 a are formed in the deformable electrode 111, the space under thedeformable electrode 111 is sealed by the protective film 112 or 412 a.

[0068] As described above, in this embodiment as well, in the surfaceshape recognition sensor for which a hollow structure can easily beformed by forming the opening portions in the deformable electrode 111,as shown in FIG. 4B or 4C, the protective film can more easily be formedon the deformable electrode by a generally used method, i.e., CVD,plasma CVD, or ozone TEOS, that is easy to apply.

[0069] <Third Embodiment>

[0070] In the surface shape recognition sensor shown in, e.g., FIG. 3B,if the pressure from an object such as a finger to be subjected tosurface shape recognition is too large, the deformable electrode (upperelectrode) may be excessively deflected and come into contact with thelower electrode to cause short-circuit. To prevent this, the uppersurface of the lower electrode is covered with a dielectric film, aswill be described below.

[0071] Main part of a method of manufacturing a surface shaperecognition sensor according to this embodiment will be described below.

[0072] First, the same processes as shown in FIGS. 1A to 1D areexecuted. Then, as shown in FIG. 5A, a lower electrode 104 a having agold upper layer and a support electrode 106 a insulated and isolatedfrom the lower electrode 104 a are formed on a substrate 101.

[0073] Next, as shown in FIG. 5B, a 0.1-μm thick dielectric film 501made of a silicon oxide film is formed by ECR (Electron CyclotronResonance) plasma CVD (Chemical Vapor Deposition). The silicon oxidefilm is formed by using, as source gases, SiH₄ and O₂ gases and settingthe flow rates of the gases to 10 and 20 sccm, respectively, and themicrowave power to 200 W. The dielectric film 501 is not limited to asilicon oxide film. Instead, another insulating material such as asilicon nitride film may be used.

[0074] As shown in FIG. 5C, a 1-μm thick resist pattern 502 is formed ina region on the dielectric film 501 above the lower electrode 104 a toentirely cover the lower electrode 104 a. The resist pattern 502 isformed by known photolithography. After that, the dielectric film 501 isselectively etched using the resist pattern 502 as a mask. In thisetching, dry etching is performed using CHF₃ gas and O₂ gas as etchinggases. The gas flow rates are set to 30 and 5 sccm, and the microwavepower is set to 300 W. As a result, an electrode dielectric film 501 athat covers the lower electrode 104 a is formed, as shown in FIG. 5D.

[0075] After this, in accordance with the same procedure as shown inFIGS. 1E to 3B, a deformable electrode 111 is formed in a region abovethe lower electrode 104 a, a protective film 412 a is formed to coverthe deformable electrode 111, and a projection 113 is formed on theprotective film 412 a, as shown in FIG. 5E. Alternatively, in accordancewith the same procedure as shown in FIGS. 1E to 2F and 4A to 4C, thedeformable electrode 111 may be formed in a region above the lowerelectrode 104 a, the protective film 412 a may be formed to cover thedeformable electrode 111, and the projection 113 may be formed on theprotective film 412 a, as shown in FIG. 5E.

[0076] According to this surface shape recognition sensor, the electrodedielectric film 501 a is formed on the lower electrode 104 a. Hence,even when the deformable electrode 111 is largely deflected downward,the lower portion of the deformable electrode 111 is prevented fromcoming into electrical contact with the lower electrode 104 a.

[0077] To prevent the contact between the lower electrode 104 a and thedeformable electrode 111, the interval between these electrodes isincreased more than necessity. This may decrease the resultantelectrostatic capacitance and degrade the sensitivity. However,according to the surface shape recognition sensor shown in FIG. 5E,since the interval between the lower electrode and the deformableelectrode can be reduced, the sensitivity is not degraded. When theinterval is increased, and an excess pressure is applied to thedeformable electrode 111 in this state, the deformable electrode 111 maycause plastic deformation and be unable to return to the original state.However, the surface shape recognition sensor shown in FIG. 5E can alsosuppress this problem.

[0078] In this embodiment as well, in the surface shape recognitionsensor for which a hollow structure can easily be formed by forming theopening portions in the deformable electrode 111, the protective filmcan more easily be formed on the deformable electrode by a generallyused method that is easy to apply.

[0079] Another method of manufacturing the electrode dielectric filmwill be described next.

[0080] First, as in the above-described embodiments, a 5-μm thick resistpattern 103 having an opening portion 103 a is formed on a seed layer102, as shown in FIG. 6A. After the resist pattern 103 is formed, a 1-μmthick metal pattern 104 made of a gold plating film is formed on theseed layer 102 exposed to the opening portion 103 a by electroplating.

[0081] In this embodiment, after that, a 0.3-μm thick dielectric film601 made of a silicon oxide film is formed using ECR plasma CVD withoutremoving the resist pattern 103 (FIG. 6B). In this case as well, thesilicon oxide film is formed by using, as source gases, SiH₄ and O₂gases and setting the flow rates of the gases to 10 and 20 sccm,respectively, and the microwave power to 200 W.

[0082] Next, the resist pattern 103 is removed. At this time, a portionof the dielectric film 601, which is in contact with the resist pattern103, is removed by lift-off. Consequently, only a dielectric film 601 aon the metal pattern 104 remains (FIG. 6C). After this, as in FIG. 1C, aresist pattern 105 is formed, and a metal pattern 106 made of a goldplating film is formed by electroplating (FIG. 6D). After that, theresist pattern 105 is removed (FIG. 6E).

[0083] The seed layer 102 is selectively etched using the formed metalpatterns 104 and 106 as a mask. In this etching, first, the upper layerof the seed layer 102, i.e., the gold film is selectively removed usingan etchant containing iodine, ammonium iodide, water, and ethanol. Next,the lower layer of the seed layer 102, i.e., the titanium film isselectively removed using an HF-based etchant. At this time, thedielectric film 601 a is also etched by the HF-based etchant. However,since the thickness of the dielectric film 601 a is 0.3 μm, thedielectric film 601 a is not entirely removed while the 0.1-μm thicktitanium film is completely etched. The dielectric film 601 a remains asan electrode dielectric film 601 b (to be described below).

[0084] As a result, as shown in FIG. 6F, the lower electrode 104 ahaving a gold upper layer, the electrode dielectric film 601 b on thelower electrode 104 a, and the support electrode 106 a insulated andisolated from the lower electrode 104 a and electrode dielectric film601 b are formed on the substrate 101.

[0085]FIG. 6F corresponds to the state shown in FIG. 5D. Then, inaccordance with the same procedure as in FIGS. 1E to 3B, the surfaceshape recognition sensor shown in FIG. 5E is formed. Alternatively, inaccordance with the same procedure as shown in FIGS. 1E to 2F and 4A to4C, the surface shape recognition sensor as shown in FIG. 5E may beformed.

[0086] In this embodiment, a silicon oxide film has been exemplified asthe dielectric film 601. However, any other insulating material such asa silicon nitride film may be used as long as it is not etched inetching the gold, titanium, and sacrificial films or it is etched onlyin a small amount.

[0087] According to this surface shape recognition sensor, the electrodedielectric film is formed on the lower electrode. Hence, even when thedeformable electrode is largely deflected downward, the lower portion ofthe deformable electrode is prevented from coming into electricalcontact with the lower electrode. To prevent the contact between thelower electrode and the deformable electrode, the interval between theseelectrodes is increased more than necessity. This may decrease theresultant electrostatic capacitance and degrade the sensitivity.However, according to the surface shape recognition sensor shown in FIG.5E, since the interval between the lower electrode and the deformableelectrode can be reduced, the sensitivity is not degraded. When theinterval is increased, and an excess pressure is applied to thedeformable electrode in this state, the deformable electrode may causeplastic deformation and be unable to return to the original state.However, the surface shape recognition sensor of this embodiment canalso suppress this problem.

[0088] In this embodiment as well, in the surface shape recognitionsensor for which a hollow structure can easily be formed by forming theopening portions in the deformable electrode, the protective film canmore easily be formed on the deformable electrode by a generally usedmethod that is easy to apply.

[0089] The electrode dielectric film may be formed in the following way.

[0090] As in the above-described embodiments, the 5-μm thick resistpattern 103 having the opening portion 103 a is formed on the seed layer102, as shown in FIG. 7A. After the resist pattern 103 is formed, the1-μm thick metal pattern 104 made of a gold plating film is formed onthe seed layer 102 exposed to the opening portion 103 a byelectroplating.

[0091] In this embodiment, next, the resist pattern 103 is removed.Then, a 0.1-μm thick dielectric film 701 made of a silicon oxide film isformed on the seed layer 102 to cover the metal pattern 104. Thedielectric film 701 is formed in accordance with the same procedure asthat for the dielectric film 501 shown in FIG. 5B.

[0092] As shown in FIG. 7C, a 1.0-μm thick resist pattern 702 is formedon the metal pattern 104 in a region on the dielectric film 701 by knownphotolithography. After the resist pattern 702 is formed, the dielectricfilm 701 is selectively etched and removed using the resist pattern 702as a mask (FIG. 7D). In this dry etching, CHF₃ gas and O₂ gas are usedas etching gases, the gas flow rates are set to 30 and 5 sccm,respectively, and the microwave power is set to 300 W. Next, the resistpattern 702 is removed, thereby forming an electrode dielectric film 701a formed from a silicon oxide film on the metal pattern 104, as shown inFIG. 7E.

[0093] After that, as in FIG. 1C, a resist pattern is formed, and themetal pattern 106 made of a gold plating film is formed byelectroplating (FIG. 7F). The resist pattern is removed (FIG. 7G). FIG.7G corresponds to the state shown in FIG. 5D. Then, in accordance withthe same procedure as in FIGS. 1E to 3B, the surface shape recognitionsensor shown in FIG. 5E is formed. Alternatively, in accordance with thesame procedure as shown in FIGS. 1E to 2F and 4A to 4C, the surfaceshape recognition sensor as shown in FIG. 5E may be formed.

[0094] The dielectric film 701 may also be formed from any otherinsulating material such as a silicon nitride film as long as it is notetched in etching the gold, titanium, and sacrificial films or it isetched only in a small amount.

[0095] In this surface shape recognition sensor as well, the electrodedielectric film is formed on the lower electrode. Hence, even when thedeformable electrode is largely deflected downward, the lower portion ofthe deformable electrode is prevented from coming into electricalcontact with the lower electrode. To prevent the contact between thelower electrode and the deformable electrode, the interval between theseelectrodes is increased more than necessity. This may decrease theresultant electrostatic capacitance and degrade the sensitivity.However, according to the surface shape recognition sensor shown in FIG.5E, since the interval between the lower electrode and the deformableelectrode can be reduced, the sensitivity is not degraded. When theinterval is increased, and an excess pressure is applied to thedeformable electrode in this state, the deformable electrode may causeplastic deformation and be unable to return to the original state.However, the surface shape recognition sensor of this embodiment canalso suppress this problem.

[0096] In this embodiment as well, in the surface shape recognitionsensor for which a hollow structure can easily be formed by forming theopening portions in the deformable electrode, the protective film canmore easily be formed on the deformable electrode by a generally usedmethod that is easy to apply.

[0097] The operation of the surface shape recognition sensor whosemanufacturing process has been described in the above embodiments willbe described next.

[0098]FIGS. 8A and 8B show the operation principle of the surface shaperecognition sensor. An object such as a finger to be subjected tosurface shape recognition is pressed against sensor chips that aretwo-dimensionally arrayed on the surface shape recognition sensor. Atthis time, a recess of the object having a three-dimensional patterndoes not come into contact with the surface shape recognition sensor(FIG. 8A). On the other hand, a projection of the object comes intocontact with the upper portion of the surface shape recognition sensorto apply a pressure to the projection 113 (FIG. 8B). The deformableelectrode 111 is deflected in accordance with the magnitude of thepressure.

[0099] When the deformable electrode 111 is deflected, the electrostaticcapacitance formed between the deformable electrode 111 and the lowerelectrode 104 a increases. The increase amount of the electrostaticcapacitance is detected by an integrated circuit (not shown) on thesubstrate 101. In addition, the change amount of the electrostaticcapacitance is converted into halftone data to detect the surface shape.

[0100] In this operation, if a large external force is applied, thedeformable electrode 111 is deflected toward the lower electrode 104 a.According to this embodiment, since the electrode dielectric film 501 ais formed, the deformable electrode 111 can be prevented from cominginto contact with the lower electrode 104 a.

[0101] Hence, any short-circuit between the deformable electrode 111 andthe lower electrode 104 a due to contact can be avoided. Additionally,the metal surfaces of the deformable electrode 111 and lower electrode104 a are prevented from coming into tight contact with each other.

[0102] Furthermore, since the electrode dielectric film 501 a is made ofa dielectric material, the change amount of the electrostaticcapacitance formed between the deformable electrode 111 and the lowerelectrode 104 a can be increased. When the electrode dielectric film 501a is set to an appropriate thickness, and an upper limit is given to thedeformable depth of the deformable electrode 111, any mechanical fatigueand destruction of the deformable electrode 111 due to deformation canbe prevented.

[0103] An electrode dielectric film design method for realizing theabove advantages will be described next. For the simplicity, as shown inFIG. 9A, an axis is set while defining the direction in which thedeformable electrode 111 is deflected as a positive direction and anorigin at the center of the deformable electrode 111 when no pressure isapplied. Let t be the thickness of the electrode dielectric film 501 a,and (d−t) be the interval between the deformable electrode 111 and theelectrode dielectric film 501 a. In addition, let x be the position atwhich the deformable electrode 111 is deflected by an external pressure,as shown in FIG. 9B.

[0104] First, a case wherein the deformable depth (d−t) of thedeformable electrode (upper electrode) 111 is set constant, and thethickness of the electrode dielectric film 501 a is changed, as shown inFIGS. 10A, 10B, and 10C, will be examined. FIG. 10D shows a change inelectrostatic capacitance in this state when the deformable electrode111 is moved from a position x=0 to a position x=d−t. As is apparentfrom FIG. 10D, the thinner the electrode dielectric film 501 a becomes,the wider the dynamic range of the electrostatic capacitance becomes.

[0105] Next, a case wherein the thickness of the electrode dielectricfilm 501 a is set constant, and the deformable depth of the deformableelectrode 111 is changed (d₁−t<d₂−t<d₃−t), as shown in FIGS. 1A, 11B,and 11C, will be examined. FIG. 11D shows a change in electrostaticcapacitance in this state when the deformable electrode 111 is movedfrom x=0 to a possible value.

[0106] To make the device function as a sensor, the deformable electrodemust deform when a pressure is applied and return to the original statebefore deformation when no pressure is applied. The deformable electrodehas a certain threshold value. When the deformation amount has thatvalue or less, elastic deformation occurs so that the deformableelectrode can return to the original state. However, when thedeformation amount exceeds that value, plastic deformation occurs, andthe deformable electrode cannot return to the original state.

[0107] Referring to FIG. 1D, the moving amount of the deformableelectrode, which serves as the threshold value between elasticdeformation and plastic deformation, is represented by d−t. When0≦x≦d₂−t, elastic deformation occurs. When d₂−t≦x, plastic deformationoccurs. Hence, even when d=d₃, i.e., the distance between the deformableelectrode 111 and the electrode dielectric film 501 a is large, thedeformable range of the sensor is 0≦x≦d₂−t. For this reason, the dynamicrange of the electrostatic capacitance is maximized when d=d₂, as isapparent from FIG. 11D. That is, the dynamic range is maximized when thedeformable electrode can deform at maximum within the range of elasticdeformation.

[0108] A case wherein the thickness of the electrode dielectric film 501a and the deformable depth of the deformable electrode 111 are setconstant, and a dielectric constant ∈ of the electrode dielectric filmis changed will be examined. When electrode dielectric films havingdifferent permittivities ∈₃<∈₂<∈₁ are used, as shown in FIGS. 12A, 12B,and 12C, the electrostatic capacitances have dynamic rangescorresponding to the permittivities, as shown in FIG. 12D. That is, thehigher the dielectric constant of the electrode dielectric film becomes,the wider the dynamic range of the electrostatic capacitance in thesensor becomes.

[0109] The shape of the electrode dielectric film 501 a will bedescribed next. Both the lower electrode 104 a and electrode dielectricfilm 501 a are formed into square shapes, and an axis is set by definingthe centers of the squares as an origin, as shown in FIG. 13A. FIG. 13Bshows the lower electrode 104 a and electrode dielectric film 501 a inFIG. 13A, which are viewed from the upper side. The lower electrode 104a has a square shape having sides b, and the electrode dielectric film501 a has a square shape having sides a.

[0110]FIG. 13C shows the electrostatic capacitance formed between thelower electrode 104 a and the deformable electrode 111 in this structurewhen a is increased from 0. The electrostatic capacitance when 0≦a≦b anda=a₁ is smaller than that when a=b. The electrostatic capacitance whena>b and a=a₂ equals that when a=b. In a region where a>b, theelectrostatic capacitance between the lower electrode 104 a and thesupport electrode 106 a undesirably increases.

[0111] For the above reasons, the electrode dielectric film 501 a isformed to appropriately cover the lower electrode 104 a. In the actualprocess, since it is difficult to form the electrode dielectric film andlower electrode into completely congruent shapes, a margin of about 1 μmis taken into consideration. In FIGS. 13A, 13B, and 13C, the lowerelectrode 104 a is assumed to have a square shape. However, the abovefacts can apply even to a structure having another shape.

[0112] The above description will be summarized. To amplify and detectthe difference between the external recess and projection at a highsensitivity, the dynamic range of the electrostatic capacitance ispreferably wide. For this purpose, the electrode dielectric film 501 ais formed as thin as possible. The electrode dielectric film is formedinto a shape congruent with the lower electrode 104 a. The surface ofthe electrode dielectric film 501 a is formed at a position at which thedeformable electrode 111 does not exceed the limit of elasticdeformation.

[0113] In the above-described embodiments, the opening portions 111 aare laid out at the four corners of a rectangular region (cell region)of the deformable electrode 111, which is surrounded by thelattice-shaped support electrode 106 a, as shown in FIG. 2F. However,the present invention is not limited to this.

[0114] For example, as shown in FIG. 14A, in addition to the openingportions 111 a laid out at the four corners, opening portions 111 b maybe laid out on the line segments of a polygon defined by the openingportions 111 a serving as vertices in a cell region of the deformableelectrode 111. Alternatively, as shown in FIG. 14B, opening portions 111c may be laid out at two opposing corners in a cell region of thedeformable electrode 111. The area of each opening portion 111 c is setto be larger than that of the opening portion 111 a or 111 b.

[0115] Opening portions formed in the deformable electrode (upperelectrode) to remove the sacrificial film is laid out in a region otherthan regions on the main part of the lower electrode and on the supportelectrode, as described above. It is only necessary that the movement ofthe deformable electrode is not impeded even when the material of theprotective film enters the space under the deformable electrode from theopening portions that are thus formed in the deformable electrode. Forexample, when the opening portions only partially overlap the upper edgeportion of the lower electrode, the movement of the deformable electrodeis not impeded by the part of the protective film that has entered fromthe opening portions.

[0116] As has been described above, according to the present invention,since the opening portions of the upper electrode, which are formed toremove the sacrificial film under the upper electrode, are laid out in aregion other than regions above the main part of the lower electrode andon the support electrode, the protective film can more easily be formedon the upper electrode by a generally used method such as coating or CVDthat is easy to apply.

What is claimed is:
 1. A surface shape recognition sensor comprising: aplurality of capacitive detection elements formed from lower electrodesand a deformable plate-like upper electrode made of a metal, the lowerelectrodes being insulated and isolated from each other and stationarilylaid out on a single plane of an interlevel dielectric formed on asemiconductor substrate, and the upper electrode being laid out abovethe lower electrodes at a predetermined interval and having a pluralityof opening portions; a support electrode laid out around the lowerelectrodes while being insulated and isolated from the lower electrodes,and formed to be higher than the lower electrodes to support the upperelectrode; and a protective film formed on the upper electrode to closethe opening portions, wherein the opening portions of the upperelectrode are laid out in a region other than regions on a main part ofthe lower electrode and on said support electrode.
 2. A sensor accordingto claim 1, wherein the opening portions of the upper electrode are laidout in a region other than a region on the lower electrode and a regionon said support electrode.
 3. A sensor according to claim 1, furthercomprising a projection laid out in a region on said protective filmabove the lower electrode.
 4. A sensor according to claim 1, whereinsaid support electrode is made of a metal.
 5. A sensor according toclaim 1, wherein said sensor comprises an electrode dielectric film laidout on the lower electrode, and the upper electrode is laid out abovesaid electrode dielectric film at a predetermined interval.
 6. A sensoraccording to claim 5, wherein letting A be a moving amount of a centralportion of the upper electrode when the upper electrode deforms atmaximum within an elastic deformation range, the interval between theupper electrode and said electrode dielectric film is not more than A.7. A sensor according to claim 5, wherein said electrode dielectric filmis formed into substantially the same shape as that of the lowerelectrode and laid out to cover the lower electrode.
 8. A method ofmanufacturing a surface shape recognition sensor, comprising the stepsof: forming an interlevel dielectric on a semiconductor substrate;forming a first metal film on the interlevel dielectric; forming a firstmask pattern having an opening portion in a predetermined region on thefirst metal film; forming a first metal pattern on a surface of thefirst metal film exposed to a bottom portion of the opening portion ofthe first mask pattern by plating; after the first mask pattern isremoved, forming a second mask pattern having an opening portion laidout around the first metal pattern on the first metal film and firstmetal pattern; forming a second metal pattern thicker than the firstmetal pattern on the surface of the first metal film exposed to a bottomportion of the opening portion of the second mask pattern by plating;after the second mask pattern is removed, etching and removing the firstmetal film using the first and second metal patterns as a mask to form alower electrode formed from the first metal film and first metal patternand a support electrode formed from the first metal film and secondmetal pattern; forming a sacrificial film on the interlevel dielectricto cover the lower electrode while keeping an upper portion of thesupport electrode exposed; forming, on the sacrificial film and supportelectrode, an upper electrode having opening portions in a region otherthan a region on the lower electrode and a region on the supportelectrode; after the upper electrode is formed, selectively removingonly the sacrificial film through the opening portions; and after thesacrificial film is removed, forming a protective film on the upperelectrode, wherein a plurality of capacitive detection elements eachhaving the lower electrode and upper electrode are formed.
 9. A methodaccording to claim 8, wherein the opening portions of the upperelectrode are formed to be laid out in a region other than a region onthe lower electrode and a region on the support electrode.
 10. A methodaccording to claim 8, wherein the protective film is formed by coating aresin onto the upper electrode.
 11. A method according to claim 8,wherein after the sacrificial film is removed, a film of an inorganicinsulating material is formed on the upper electrode by vapor depositionand etched back to form the protective film.
 12. A method according toclaim 8, further comprising the steps of forming a resin film havingphotosensitivity on the protective film, and exposing and developing apredetermined region of the resin film to form a projection in a regionabove the lower electrode.
 13. A method according to claim 8, whereinafter the lower electrode and support electrode are formed, a firstdielectric film that is lower than the support electrode and covers thelower electrode is formed on the lower electrode, the first dielectricfilm is selectively removed to form an electrode dielectric film on thelower electrode, and after the electrode dielectric film is formed, thesacrificial film is formed.
 14. A method according to claim 8, whereinafter the first metal pattern is formed, a first dielectric film isformed on the first metal pattern to cover the first metal pattern, thefirst mask pattern is removed to form an electrode dielectric film onthe first metal pattern, and after the electrode dielectric film isformed, the second mask pattern having the opening portion laid outaround the first metal pattern is formed on the metal film and electrodedielectric film.
 15. A method according to claim 8, wherein after thefirst mask pattern is removed, a first dielectric film is formed on thefirst metal pattern to cover the first metal pattern, the firstdielectric film is selectively removed to form an electrode dielectricfilm on the first metal pattern, and after the electrode dielectric filmis formed, the second mask pattern having the opening portion laid outaround the first metal pattern is formed on the metal film and electrodedielectric film.